The present invention relates in general to filtering apparatus and, in particular to a new and useful filtering and backwash apparatus, particularly for filtering water supplied to a house.
Such filter apparatus are known per se. Their inlet is connected to the house water main and their outlet leads to the points of utilization. They prevent soiling matter entrained by the water, such as sand, and other particles, from penetrating to the consuming points and causing trouble or even damages. The main filter is passed by the water permanently in the same direction, so that dirt, etc. becomes deposited on the upstream side of the filter. The more the filter is choked with extraneous matter, the higher the resistance to flow becomes and the pressure drop in the filter. To restore the initial state, the filtering apparatus must be cleaned from time to time. This is advantageously done by reversing the flow through the filter, for which purpose the design is suitably adapted. During the reversal or back-flushing, the flow is directed against the down-stream side of the filter, so that the initial upstream side now becomes the downstream side. Due to this reversal of flow through the filter, dirt deposits or the like are broken away and drained along with the wash water through an outlet which has been open during the back-flush operation. Advantageously, the outlet of the filter remains closed during this time, which may be done simultaneously with the reversal to back-flush.
As a rule, the pressure in the house water main is predetermined, i.e. it cannot be varied. Further, requirements on the purity of water determine the mesh size of the filter. On the other hand, the velocity of water flow through the filter depends on the pressure in the piping and on the size of the screen apertures. This means that the purifying effect during the back-flush is greater in more choked filters than in less choked ones where the passages through the filter have not yet been too strongly reduced. This is related to the fact that with a reduction of the sectional area of the individual screen apertures, the flow velocity therethrough increases and that with an increased flow velocity, the adhering particles are more easily broken away than at a relatively slower velocity.
Even with a heavily clogged screen, an unfavorable cleaning effect may be obtained if, first, larger portions of the dirt layer are broken away at different locations and the flushing water then flows only through these exposed portions of the filter while the other, still heavily clogged filter portions hardly allow any passage of water.